Boots are well-known devices used to enclose an end of a constant velocity joint. Boots keep out dirt, debris and moisture from the joint and keep lubricant in the joint.
One example of a prior art boot 10 for a joint 12 is depicted in FIG. 1. The joint 12 comprises an inner race 14, an outer race 16, a cage 18 and at least one ball 20 within the cage 18.
The boot 10 encloses one end of the joint 12. The boot 10 is connected at one end to the outer race 16 with a boot can 22. A boot bead 26 is formed on the boot can 22 to capture the boot 10. The boot bead 26 is generally round and formed inwardly. A boot can crimp 28 also helps hold the boot 10 in place. The boot can crimp 28 is also formed inwardly. The boot 10 is connected at the other end to a shaft 24, such as by a clamp 30.
The size of the boot 10 used in FIG. 1 is characterized by boot length L, boot can length LL, boot can inner diameter Ø Db and the thickness of the boot 10. Boot length L, boot can length LL and boot can inner diameter Ø Db are determined by the required maximum static articulation angle capability, which is depicted in FIG. 2. More particularly, boot length L is determined in a way that boot length L in a joint assembly state as shown in FIG. 1 is equivalent to the boot length of an extended boot region 32 and the boot length of a contracted boot region 34 at a maximum joint angle.
Boot thickness for the boot 10 of FIGS. 1 and 2 is depicted in FIG. 3. The boot 10 generally has a round shape RR with an angle α from the horizontal, where the thickness T1 of an upper slope portion 36, is equal to the thickness T2 of a concave portion 38, which is equal to the thickness T3 of a lower slope portion 40. The joint boot thickness T1, T2, T3 is determined by taking into consideration boot radial and axial stiffness related to potential high risk boot failure modes, such as boot inversion and boot folding, both of which mainly occur at high joint internal pressures. Line Ø Dg represents the typical grease fill level for such a joint 12.
FIGS. 4-8 depict another prior art constant velocity joint 42 with a boot 44. The joint 42 comprises an inner race 46, an outer race 48, a cage 50 and at least one ball 52 within the cage. This joint 42 uses a sleeve 54 that couples the inner race 46 with a pinion shaft 56. A nut 58 connects the sleeve 54 to the pinion shaft 56.
The sleeve 54 in such a direct pinion mount design has a larger diameter Ds1 than a tube shaft diameter Ds in a non-direct pinion mount design, such as shown in FIGS. 1-3. Therefore, the boot can inner diameter Db1 should increase by the difference between Ds1−Ds to have the equivalent maximum static joint angle capability to that of a non-direct pinion mount design, such as in FIGS. 1-3. This results in a higher grease pressure acting on the direct pinion mount boot 44 compared with the pressure on the boot 10 depicted in FIG. 1.
The boot length L1 is limited by the nut 58 as shown in FIG. 4, therefore, it is more difficult to make the boot length L1 equivalent to the non-direct pinion mount joint boot length L depicted in FIG. 1. This results in a boot can inner diameter Db1 being bigger to have the equivalent boot overall length required for achieving a maximum joint angle compared to the design in FIG. 1.
Further, the limited boot axle length L1 cannot provide a sufficient press fit contact portion 62 between the sleeve 54 and the boot 44, which causes region 64 near a boot groove seat 66 to be bumped up and tilted toward the boot groove seat 66 by a crimping force of a boot clamp 68 acting on the boot clamp seat inside corner 70, which can be appreciated from FIGS. 6 and 7.
FIG. 8 depicts a direct pinion mount joint 42 having uniform boot thickness (T21=T22=T23) that has folded/self-contacted at a boot contacted region 78 as a result of the wrong boot thickness for this design. The figure also depicts the boot 44 being severely bent at an edge of the boot can crimp 80 by high grease pressure while operating at a high temperature, a high operating speed and at a high operating angle.
In view of the disadvantages of attempting to apply a non-direct pinion mount boot system to a direct pinion mount boot system, a new design is required.